1. Field of the Invention
The present invention relates to a semiconductor memory device, and more particularly, to a programming section of a semiconductor memory device having a fuse read only memory (fuse ROM).
2. Discussion of the Related Art
FIG. 1 illustrates a fuse ROM for a conventional semiconductor memory device. A fuse FUSE1 is composed of a resistive component which can be opened in a wafer state with a laser cutting machine. An inverting device INV1 and a transistor M1 are connected to the fuse FUSE1 for latching the state of a contact node N1 of the fuse FUSE1.
The operation of the above conventional fuse ROM will now be described. If the fuse FUSE1 is connected, the node N1 has a high level, and the output OUT becomes a zero state. On the other hand, if the fuse FUSE1 is opened, the node N1 is discharged to a low level through the transistor M1 driving the output OUT to a `1` state. That is, the output depends on the connection or disconnection of the fuse. If the fuse is cut off, the output terminal produces `1`. If the fuse is not cut off, an output `0` is produced.
However, in this conventional fuse ROM, if power is supplied to the chip, the fuse FUSE1 latches, and, at the instant when the power is supplied, a considerably large current I1 flows through the fuse FUSE1 and the transistor M1 when the state of the chip is unstable, resulting in a prolonged continuation of the unstable state. Particularly, a large capacity memory device is provided with a considerably large number of fuse ROMs for redundant memory blocks. Therefore, the sum of the unstable currents I1 totals several tens of mA. Furthermore, if the fuse FUSE1 is cut by a laser cutting machine and the fuse FUSE1 is not completely opened and remains in a connected state, a leakage current continuously flows to the node N1. As a result, such leakage current represents a considerable portion of the total leakage current. In such a case, the following problems occur. The output OUT does not represent an open state of the fuse FUSE1, but is latched to a value corresponding to a connected state of the fuse. Furthermore, the power consumption of the memory device at the standby state is increased, and therefore, the memory device becomes unsuitable for low power applications.